Using a permenant dye over another dye.....will it work or look cack?

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My hair is about 2" long on the crown (that's the longest bit) I don't know whether to have it cut before Christmas or not.

I dyed it after the last cut (about last week in October) , I use a permenant coppery brown which gives it a mid brown auburn look.

I bought some slightly redder coppery brown (same brand) - if I over-layer will the new colour take all over?
It's not a huge difference but my new growth will take the colour well (some grey)

I need a strand test really don't I?

Cut and dye?
Dye it and leave the length as it is (with the back-up of a brownish dye if I need to ).
Not worried too much about using dye two days running, it gets cut out.

What d'you think?

Ahhhhhhhh no-one cares if I look stripey

I'm going to have it chopped this week, so old-dye-be-gone and new hair be reddish.

My hair has done the nice-to-unworkable turnaround in the space of 36 hours

If you use a colour that is at the same level but redder (say a 5.5 over a 5.3) then it will take and cover. Same if it is a couple of shades lighter and you are dyeing it darker.

The problem of root glow arises if you try to put a lighter shade over a darker one. You need to check out the shade numbers.

The dyes are both Superdrug but I reckon the new one is a lighter red .
I'm going to get the hairdresser to chop out the old dye ( then I might have a tiny amount of darker tips but it'll only be on the top/crown. Could be nice, if not, I can wear a hat I can run a semi-perm over it.